Sealed Nuclear Reactors and Private Atomic Rockets.

[ikrase]

Here are thoughts that prompted this


Single Stage to Orbit is barely possible with chemical fuels.

It is not too bad with nuclear power. We're talking Nerva, DUMBO, Nuclear Lightbulb, etc. I think that these can be made acceptably safe.

Mass ratios are about 3 or 4, and could be made better with heavy research.

A homebuilt chemical-powered orbital shuttle is impossible unless you can just equal NASA budget because of the huge mass ratio problem.

And then there's the fact that some isolated communities have tiny hot tub sized nuclear reactors that are totally sealed and have no operators.

Do you think it would be feasible to make sealed NERVA cores for private possession, or something like this?

 

[n72.75]

Short answer: Yes

Long answer:
People would need to get over their fear of nuclear power before anything like that would be acceptable. Also, nuclear reactors aren't cheep, and private aerospace corporations would be able to launch much cheaper then NASA because they would be driven by free market principals.

 

[ikrase]

Point one: I disdain free market. They are partly responsible for the high prices of space lift. But this is not my time to argue that point.

Point Two: this assumes less fear of nukes, but still precautions about started reactors crashing, or terrorist abombs.

Just what is the minimum cost of a NERVA reactor, I wonder (the cost to make several large reactors, per reactor, not the cost of development.)

Could it possibly be less than 100K dollars for a reactor engine and the first set of fuel rods?

 

[Andy44]

Political reality short answer: no. Politically not possible.

Engineer's short answer, maybe. The US Army nuclear power program experimented with lightweight, portable nuclear reactors between 1950 and 1975 or so. The results were mixed. One of the lightweight reactors (called SL-1) was poorly designed with a single control rod in the middle of the core, and resulted in a hideous accident that killed 3 men and ended with a massive cleanup.

Other experimental reactors worked fine, but the Army found it impractical to field portable reactor powerplants to the field.

Accidents will happen, it's a statistical certainty. If you allow lisenced reactor operators to use reactors with strict oversight and flight safety envelopes over water, you can minimize accidents and their effects, but you can't eliminate them.

And the cost effectiveness of it is driven down by the cost of safety measures. Nuclear power is good, but it's not easy.

 

[ikrase]

These hot tub size reactors _exist_. Now.

and do not have staff, I believe. They might have remote shutdown or something. Dont know. They are pre-started so they are too hot for someone to steal the fuel.

To me it seems like it might be possible to make individual fuel elements of a small fuel element NTR reactor reentry and crash resistant.

 

[Andy44]

Perhaps you could provide a link to one of these unattended hot tub reactors, because frankly I don't believe anyone would leave a nuclear reactor alone without supervision. Perhaps I am wrong.

Anyway, if those exist, they are likely low power reactors, whereas a NERVA is a different animal.

 

[PhantomCruiser]

These hot tub size reactors _exist_. Now.

:link: please...

I also wonder what the cost of one of these would run. I do know that a 1200MW unit cost above 3 Billion. That's electrical power, thermal power is about the same...

 

[ikrase]

an alaskan town is looking at one. Hyperion is one of the groups.

http://www.guardian.co.uk/environment/2008/nov/09/miniature-nuclear-reactors-los-alamos

I wonder just how inexpensive a reactor can get.

 

[sputnik]

Certainly, sealed nuclear reactors like the Hyperion one will be key to the solar system. You need one for a moon base, for example.
But that system wouldn't work well as an open-cycle NERVA-type design. As a power source for an electric propulsion system, sure, although most nuclear-electric drives are far too slow....

But a nuclear SSTO? This is not an improvement.

Sure, you might THINK it is. Examining the rocket equation, you'd think that a high Isp is the way to go...but not if it comes at the cost of a whole lot of penalty dry mass. And it does.
For starters, the engine thrust/weight of a NERVA was THREE, fer gossakes. So you can just about get your SSTO to hover, if you can figure out how to make tanks, TPS, landing gear, crew module, and payload all mass zero.
And the tankage will NOT weigh zero. Liquid hydrogen is the exact opposite of dense, and tankage scales with the volume, not mass. (Well, it goes with the third power of mass, but volume is a first-order relationship).
Sure, your mass ratio is "only" 3 or 4. But getting an LH2 nuclear SSTO to a mass ratio of 3 or 4 is very very HARD. If you can develop tanks, structures, etc light enough to do that, then those same tanks and structure will make a mass ratio of 10 LOX/LH2 vehicle a piece of cake. Which means you'd do that FIRST.
Unless, as some believe, making a mass ratio 20 LOX/Kerosene vehicle turns out to be easier still....

The all-LH2 nuclear SSTO has been designed...it's called RITA. See:
http://www.astronautix.com/lvs/ritac.htm

Unfortunately, while the Astronautix description makes it sound pretty viable, I was privileged to hear Max Hunter give a talk once where he poked fun at his old design. For starters, it was the epitome of the "build 'em big" school of SSTO design, which theorizes that if you can make it big enough, all the fixed masses (crew and avionics) become very small. RITA needed the help.
Rather more seriously, RITA wouldn't have worked as designed. In 1961, the fact that engine thrust/weight also scales with propellant density was poorly understood, and the Douglas designers seriously underestimated the mass of the nuclear engines to get the thing off the ground.
Said Hunter of his own design, nuclear LH2 is absolutely the worst possible way to approach an SSTO. If you can almost make one of those close, doing it with a denser fuel is easy.

Sorry for the digression. And once in orbit, I agree that nuclear power will, eventually, be the key to the solar system. Hopefully we can leverage off the newer systems being built, and Hyperion's encapsulated units are particularly exciting for base power.

 

[jedidia]

Nuclear Lightbulb

You can forgett this one right away under any circumstances, since it has radioactive exhaust. Might do in space, but nut for lift-offs.

 

[T.Neo]

If I remember correctly, Nuclear Lightbulb constrains the radioactive nuclear material within a temperature resistant "lightbulb", hence the name.

 

[sputnik]

T. Neo is right; Nuclear Lightbulb involves a gaseous reactor core that never contacts the working fluid/propellant because they're separate by a REALLY transparent pane of REALLY high-temperature-resistant material (like maybe quartz). So the exhaust is NOT radioactive.
This is a variant of the earlier gas core reactor, where the gaseous uranium is kept contained in a magnetic field while the working fluid/propellant is just sent right through it. You do lose some uranium and fission byproducts through the exhaust that way, and the exhaust IS radioactive. A little.

So radioactive exhaust is not a reason to reject a nuclear lightbulb for use in the Earth's atmosphere; it isn't. Poor thrust/weight is, though; I've never heard of an NLB conceptual design that could lift itself in Earth's gravity.

 

[Loru]

Nice article about nuclear rockets:
http://www.nuclearspace.com/Liberty_ship_menupg.aspx

 

[RisingFury]

A homebuilt chemical-powered orbital shuttle is impossible unless you can just equal NASA budget because of the huge mass ratio problem.

Yea, and a home built nuclear reactor is TOTALLY a possibility!!1!!!!!!

And then there's the fact that some isolated communities have tiny hot tub sized nuclear reactors that are totally sealed and have no operators.

That's a fact? Or have you been watching too many movies latelly?

 

[Sky Captain]

Nuclear reactors are`t exactly cheap, especially the kind with extreme performance needed for SSTO. Such reactors does`t even exist yet and likely would take many billions of $$$ to develop. And if you nuclear rocket blows up you have a huuuuuge PR problem even if it doe`t harm anyone.

---------- Post added at 09:45 PM ---------- Previous post was at 09:41 PM ----------

Yea, and a home built nuclear reactor is TOTALLY a possibility!!1!!!!!!

If you can get your hands on sufficient quantities of enriched uranium or plutonium homebuilt nuclear reactor is easy just pile up enough fissionable material and nuclear chain reaction will start by itself (and kill you and your neighbors). Hard part is making the whole process safe and controllable.

 

[jedidia]

If I remember correctly, Nuclear Lightbulb constrains the radioactive nuclear material within a temperature resistant "lightbulb", hence the name.

ooops :embarrassed: mistook it for an other one, then.

 

[garyw]

Yea, and a home built nuclear reactor is TOTALLY a possibility!!1!!!!!!

It is. well, sort of.

http://www.dangerouslaboratories.org/radscout.html

 

[RisingFury]

It is. well, sort of.

http://www.dangerouslaboratories.org/radscout.html

Assuming it's real, a few grams of nuclear material is hardly a nuclear reactor.

If that's what you consider a nuclear reactor, then I built one in school in my experiment class...

 

[T.Neo]

If that's what you consider a nuclear reactor, then I built one in school in my experiment class...

Do tell.

 

[RisingFury]

Well, I had one task at uni that dealt with radioactive materials... We had some isotope of Cesium that produced Gamma, there was a bit of Uranium and a few other samples...

The task required us to measure, among other things, the temperature of the sample, click count / unit of time, shielding provided by lead, time between clicks,... the usual stuff.

One of the samples was a few degrees warmer then the room. Another one was supposed to be, but the sample was so old that the remote sensor we had couldn't pick up the difference...